[if vfmt] function attribute for skipping functions for performance

vlib/compiler/main.v

@@ -113,6 +113,7 @@ pub mut:
 						 // This is on by default, since a vast majority of users do not
 						 // work on the builtin module itself.
 	//generating_vh bool
+	comptime_define string  // -D vfmt for `if $vfmt {`
 }
 
 // Should be called by main at the end of the compilation process, to cleanup
@@ -765,6 +766,7 @@ pub fn new_v(args[]string) &V {
 
 	joined_args := args.join(' ')
 	target_os := get_arg(joined_args, 'os', '')
+	comptime_define := get_arg(joined_args, 'd', '')
 	mut out_name := get_arg(joined_args, 'o', 'a.out')
 
 	mut dir := args.last()
@@ -922,6 +924,7 @@ pub fn new_v(args[]string) &V {
 		cflags: cflags
 		ccompiler: find_c_compiler()
 		building_v: !is_repl && (rdir_name == 'compiler' || rdir_name == 'v.v'  || dir.contains('vlib'))
+		comptime_define: comptime_define
 	}
 	if pref.is_verbose || pref.is_debug {
 		println('C compiler=$pref.ccompiler')

vlib/compiler/parser.v

@@ -3872,7 +3872,13 @@ fn (p mut Parser) js_decode() string {
 
 fn (p mut Parser) attribute() {
 	p.check(.lsbr)
+	if p.tok == .key_if {
+		// [if vfmt]
+		p.next()
+		p.attr = 'if ' + p.check_name()
+	}	else {
 		p.attr = p.check_name()
+	}
 	attr_token_idx := p.cur_tok_index()
 	if p.tok == .colon {
 		p.check(.colon)

vlib/compiler/vfmt.v

@@ -7,6 +7,7 @@ module compiler
 import strings
 
 // fmt helpers
+//[if vfmt]
 fn (scanner mut Scanner) fgen(s_ string) {
 	mut s := s_
 	if scanner.fmt_line_empty {